The cardiac responses to stress and cardiomyopathy share a common feature: altered signaling through G protein-- coupled receptor (GPCR) pathways that regulate the homeostatic balance of signaling in the heart. Restoration of normal homeostasis in cardiomyopathy is the basis for medical therapies that target GPCRs, such as the beta-adrenergic receptor. The common theme of the collaborative studies is to genetically alter G protein signaling pathways in order to identify the fundamental processes by which GPCRs and G proteins influence the development and/or progression of cardiomyopathy. This individual R01 is focused on specific G protein signaling pathways. In the heart, signals derived from over 20 different GPCRs are communicated through five major G protein pathways. In this proposal, cardiac-targeted, constitutive activation of specific G protein pathways are used to define the in vivo responses of the five major G protein pathways. To gain tissue-specific, temporally regulated control of G protein signals, two powerful biological approaches are combined. First, the primary signaling component of each G protein (Galpha) can be constitutively activated (Galpha*) so that each of the five major G protein pathways (Galphas*, Galphai*, Galphaq*, Galphal2*, or Galphal3*) can be examined. Second, the tetracycline transactivator (tet) system allows inducible expression of these constitutively active forms of Galpha in the adult mouse heart, avoiding possible developmental effects. Analysis of the transgenic mice will include detailed physiologic measurements and the use of DNA arrays for measuring changes in gene expression. These studies will provide answers to questions, such as: Which G protein pathway will cause cardiomyopathy? How does each G protein pathway alter the homeostatic balance of the heart? How can G protein signals be used to restore the homeostatic balance and ameliorate the pathology of an experimentally induced cardiomyopathy? A comprehensive, focused study of G protein signaling in the heart is proposed with three specific aims: 1. To selectively activate each of the major G protein signaling pathways in the heart by conditionally expressing mutationally activated Galpha subunits in transgenic mouse hearts. 2. To determine the physiological and gene expression effects of each major G protein pathway in a normal adult mouse heart. 3. To selectively activate G protein pathways in the setting of two experimentally induced cardiomyopathy models where G protein signaling has been shown to be altered. (End of Abstract)